Giant Food and Safeway and the union representing grocery workers in the Baltimore-Washington area agreed Tuesday to extend the labor contract through Dec. 20, while negotiators wrangle over issues such as health benefits.

Workers had been expected to consider a proposal as early as Wednesday, but no agreement has been reached. The 18-month contract, covering 28,000 members of the United Food & Commercial Workers union at both grocers, previously had been extended through Nov. 15.

The impact of health reform on workers' health coverage has been the biggest obstacle to reaching an agreement, said Mark P. Federici, president of UFCW Local 400, which represents workers in Maryland's Washington suburbs.

"Between this and the pervasiveness of corporate greed, virtually all bargaining in our industry across the country has resulted in lengthy delays and extensions," Federici said.

In a statement, Giant said the company is encouraged by progress at the bargaining table.

"Our focus is on securing a fair and reasonable contract that respects our company's 77-year legacy and honors our associates' contributions, while also recognizing our competitive realities," the company said.